Liquid crystal cells containing a layer of nematic liwuid crystal composition between a pair of parallel transparent plates are employed in a variety of optical installations. Such devices are used principally in digital display devices.
In my copending U.S. application Ser. No. 121,071, filed Feb. 17, 1980, now U.S. Pat. No. 4,385,806, an improved liquid crystal cell is described wherein a conductive transparent film is provided on each side of the transparent flat plates which confine the liquid crystal composition. An electrical bias voltage, AC or DC, is applied to the two thin films to permit the liquid crystal composition to respond rapidly to additional electrical voltage applied across the two conductive coatings.
It is also known that thin layers of liquid crystal composition will bring about a phase shift in a beam of polarized light which is transmitted through the liquid crystal composition. Heretofore, the devices have been employed as light shutters which block the polarized light in the regions where an electrical field is established across the liquid crystal composition. Typical turn-off times of 250-300 milliseconds are common with existing liquid crystal light shutters which employ nematic liquid crystals. Such response time is much too large to permit the use of such devices in high speed communication.
In my copending U.S. patent application Ser. No. 235,006 filed Feb. 17, 1982, now U.S. Pat. No. 4,436,376, I have provided a communications system wherein a light beam is polarized and phase-modulated for transmission to a receiving station which includes a demodulator. The transmitted light is a phase-modulated light which requires a phase splitter and a demodulator at the receiving station to convert the phase-modulated light to intelligible form. A receiving station for a phase-modulated light requires complex detection facilities.
There exists a need for simple, inexpensive, lightweight detection facilities for the phase-modulated light transmissions which have been described in my copending application Ser. No. 235,006 aforesaid.